fix: validate and parse nested models properly with default_factory

benchmarks/run.py

@@ -274,6 +274,6 @@ def diff():
     else:
         main()
 
-    if None in other_tests:
-        print('not all libraries could be imported!')
-        sys.exit(1)
+    # if None in other_tests:
+    #     print('not all libraries could be imported!')
+    #     sys.exit(1)

changes/1710-PrettyWood.md

@@ -0,0 +1 @@
+fix validation and parsing of nested models with `default_factory`

pydantic/fields.py

@@ -341,8 +341,22 @@ def prepare(self) -> None:
         e.g. calling it it multiple times may modify the field and configure it incorrectly.
         """
 
-        # To prevent side effects by calling the `default_factory` for nothing, we only call it
-        # when we want to validate the default value i.e. when `validate_all` is set to True.
+        self._set_default_and_type()
+        self._type_analysis()
+        if self.required is Undefined:
+            self.required = True
+            self.field_info.default = Required
+        if self.default is Undefined and self.default_factory is None:
+            self.default = None
+        self.populate_validators()
+
+    def _set_default_and_type(self) -> None:
+        """
+        Set the default value, infer the type if needed and check if `None` value is valid.
+
+        Note: to prevent side effects by calling the `default_factory` for nothing, we only call it
+        when we want to validate the default value i.e. when `validate_all` is set to True.
+        """
         if self.default_factory is not None:
             if self.type_ is None:
                 raise errors_.ConfigError(
@@ -368,14 +382,6 @@ def prepare(self) -> None:
         if self.required is False and default_value is None:
             self.allow_none = True
 
-        self._type_analysis()
-        if self.required is Undefined:
-            self.required = True
-            self.field_info.default = Required
-        if self.default is Undefined and self.default_factory is None:
-            self.default = None
-        self.populate_validators()
-
     def _type_analysis(self) -> None:  # noqa: C901 (ignore complexity)
         # typing interface is horrible, we have to do some ugly checks
         if lenient_issubclass(self.type_, JsonWrapper):

tests/test_edge_cases.py

@@ -1714,3 +1714,19 @@ class Config:
 
     m1 = MyModel()
     assert m1.id == 2  # instead of 1
+
+
+def test_default_factory_validator_child():
+    class Parent(BaseModel):
+        foo: List[str] = Field(default_factory=list)
+
+        @validator('foo', pre=True, each_item=True)
+        def mutate_foo(cls, v):
+            return f'{v}-1'
+
+    assert Parent(foo=['a', 'b']).foo == ['a-1', 'b-1']
+
+    class Child(Parent):
+        pass
+
+    assert Child(foo=['a', 'b']).foo == ['a-1', 'b-1']

tests/test_main.py

@@ -1174,6 +1174,36 @@ class MyModel(BaseModel):
     assert m2.id == 2
 
 
+def test_default_factory_validate_children():
+    class Child(BaseModel):
+        x: int
+
+    class Parent(BaseModel):
+        children: List[Child] = Field(default_factory=list)
+
+    Parent(children=[{'x': 1}, {'x': 2}])
+    with pytest.raises(ValidationError) as exc_info:
+        Parent(children=[{'x': 1}, {'y': 2}])
+
+    assert exc_info.value.errors() == [
+        {'loc': ('children', 1, 'x'), 'msg': 'field required', 'type': 'value_error.missing'},
+    ]
+
+
+def test_default_factory_parse():
+    class Inner(BaseModel):
+        val: int = Field(0)
+
+    class Outer(BaseModel):
+        inner_1: Inner = Field(default_factory=Inner)
+        inner_2: Inner = Field(Inner())
+
+    default = Outer().dict()
+    parsed = Outer.parse_obj(default)
+    assert parsed.dict() == {'inner_1': {'val': 0}, 'inner_2': {'val': 0}}
+    assert repr(parsed) == 'Outer(inner_1=Inner(val=0), inner_2=Inner(val=0))'
+
+
 @pytest.mark.skipif(sys.version_info < (3, 7), reason='field constraints are set but not enforced with python 3.6')
 def test_none_min_max_items():
     # None default